Define the ConfigFeatureFlagConfiguration fragment.

This will eventually be used to store the values of user-defined
configuration flags, once such a rule is added. Because this rule
does not exist yet, this fragment is currently not part of the
rule class provider. This will have to be done when that rule
is turned on.

--
PiperOrigin-RevId: 150638292
MOS_MIGRATED_REVID=150638292

3 files changed, 176 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/BUILD b/src/main/java/com/google/devtools/build/lib/BUILD
index 2ffe989c1f..d76c5566b7 100644
--- a/src/main/java/com/google/devtools/build/lib/BUILD
+++ b/src/main/java/com/google/devtools/build/lib/BUILD
@@ -29,6 +29,7 @@ filegroup(
         "//src/main/java/com/google/devtools/build/lib/rules/apple:srcs",
         "//src/main/java/com/google/devtools/build/lib/rules/apple/cpp:srcs",
         "//src/main/java/com/google/devtools/build/lib/rules/apple/swift:srcs",
+        "//src/main/java/com/google/devtools/build/lib/rules/config:srcs",
         "//src/main/java/com/google/devtools/build/lib/rules/cpp:srcs",
         "//src/main/java/com/google/devtools/build/lib/rules/cpp/proto:srcs",
         "//src/main/java/com/google/devtools/build/lib/rules/genquery:srcs",
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/BUILD b/src/main/java/com/google/devtools/build/lib/rules/config/BUILD
new file mode 100644
index 0000000000..6e480d9628
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/BUILD
@@ -0,0 +1,27 @@
+# Description:
+#   Support for rules which enable users to define configuration
+
+package(
+    default_visibility = ["//src:__subpackages__"],
+)
+
+java_library(
+    name = "config",
+    srcs = glob([
+        "*.java",
+    ]),
+    deps = [
+        "//src/main/java/com/google/devtools/build/lib:build-base",
+        "//src/main/java/com/google/devtools/build/lib/actions",
+        "//src/main/java/com/google/devtools/build/lib/cmdline",
+        "//src/main/java/com/google/devtools/common/options",
+        "//third_party:guava",
+        "//third_party:jsr305",
+    ],
+)
+
+filegroup(
+    name = "srcs",
+    testonly = 0,  # All srcs should be not test only, overwrite package default.
+    srcs = glob(["**"]),
+)
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagConfiguration.java
new file mode 100644
index 0000000000..3d751c1721
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagConfiguration.java
@@ -0,0 +1,148 @@
+// Copyright 2017 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License
+
+package com.google.devtools.build.lib.rules.config;
+
+import com.google.common.base.Optional;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ImmutableSortedMap;
+import com.google.common.hash.Hasher;
+import com.google.common.hash.Hashing;
+import com.google.devtools.build.lib.actions.ArtifactOwner;
+import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
+import com.google.devtools.build.lib.analysis.config.BuildOptions;
+import com.google.devtools.build.lib.analysis.config.ConfigurationEnvironment;
+import com.google.devtools.build.lib.analysis.config.ConfigurationFragmentFactory;
+import com.google.devtools.build.lib.analysis.config.FragmentOptions;
+import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.common.options.Converter;
+import com.google.devtools.common.options.Option;
+import java.util.Map;
+import java.util.SortedMap;
+import javax.annotation.Nullable;
+
+/**
+ * Configuration fragment for Android's config_feature_flag, flags which can be defined in BUILD
+ * files.
+ */
+public final class ConfigFeatureFlagConfiguration extends BuildConfiguration.Fragment {
+
+  /** A converter used by the flag options which always returns an empty map, ignoring input. */
+  public static final class EmptyImmutableSortedMapConverter
+      implements Converter<ImmutableSortedMap<Label, String>> {
+    @Override
+    public ImmutableSortedMap<Label, String> convert(String input) {
+      return ImmutableSortedMap.<Label, String>of();
+    }
+
+    @Override
+    public String getTypeDescription() {
+      return "n/a (do not set this on the command line)";
+    }
+  }
+
+  /** The options fragment which defines {@link ConfigFeatureFlagConfiguration}. */
+  public static final class Options extends FragmentOptions {
+    /** The mapping from config_feature_flag rules to their values. */
+    @Option(
+        name = "config_feature_flag values (private)",
+        category = "internal",
+        converter = EmptyImmutableSortedMapConverter.class,
+        defaultValue = "{}")
+    public ImmutableSortedMap<Label, String> flagValues = ImmutableSortedMap.of();
+
+    /** Retrieves the set of flag-value pairs. */
+    public ImmutableSortedMap<Label, String> getFlagValues() {
+      return this.flagValues;
+    }
+
+    /**
+     * Replaces the set of flag-value pairs with the given mapping of flag-value pairs.
+     *
+     * <p>Flags not present in the new {@code flagValues} will return to being unset! To set flags
+     * while still retaining the values already set, call {@link #getFlagValues()} and build a map
+     * containing both the old values and the new ones.
+     */
+    public void replaceFlagValues(Map<Label, String> flagValues) {
+      this.flagValues = ImmutableSortedMap.copyOf(flagValues);
+    }
+  }
+
+  /**
+   * A configuration fragment loader able to create instances of {@link
+   * ConfigFeatureFlagConfiguration} from {@link ConfigFeatureFlagConfiguration.Options}.
+   */
+  public static final class Loader implements ConfigurationFragmentFactory {
+    @Override
+    public BuildConfiguration.Fragment create(
+        ConfigurationEnvironment env, BuildOptions buildOptions) {
+      return new ConfigFeatureFlagConfiguration(buildOptions.get(Options.class));
+    }
+
+    @Override
+    public Class<? extends BuildConfiguration.Fragment> creates() {
+      return ConfigFeatureFlagConfiguration.class;
+    }
+
+    @Override
+    public ImmutableSet<Class<? extends FragmentOptions>> requiredOptions() {
+      return ImmutableSet.<Class<? extends FragmentOptions>>of(Options.class);
+    }
+  }
+
+  private final ImmutableSortedMap<Label, String> flagValues;
+  @Nullable private final String flagHash;
+
+  /** Creates a new configuration fragment from the given {@link Options} fragment. */
+  public ConfigFeatureFlagConfiguration(Options options) {
+    this.flagValues = options.getFlagValues();
+    this.flagHash = this.flagValues.isEmpty() ? null : hashFlags(this.flagValues);
+  }
+
+  /** Converts the given flag values into a string hash for use as an output directory fragment. */
+  private static String hashFlags(SortedMap<Label, String> flagValues) {
+    // This hash function is relatively fast and stable between JVM invocations.
+    Hasher hasher = Hashing.murmur3_128().newHasher();
+
+    for (Map.Entry<Label, String> flag : flagValues.entrySet()) {
+      hasher.putUnencodedChars(flag.getKey().toString());
+      hasher.putUnencodedChars(flag.getValue());
+    }
+    return hasher.hash().toString();
+  }
+
+  /**
+   * Retrieves the value of a configuration flag.
+   *
+   * <p>If the flag is not set in the current configuration, then the returned value will be absent.
+   *
+   * <p>This method should only be used by the rule whose label is passed here. Other rules should
+   * depend on that rule and read a provider exported by it. To encourage callers of this method to
+   * do the right thing, this class takes {@link ArtifactOwner} instead of {@link Label}; to get the
+   * ArtifactOwner for a rule, call {@code ruleContext.getOwner()}.
+   */
+  public Optional<String> getFeatureFlagValue(ArtifactOwner owner) {
+    return Optional.fromNullable(flagValues.get(owner.getLabel()));
+  }
+
+  /**
+   * Returns a fragment of the output directory name for this configuration, based on the set of
+   * flags and their values. It will be {@code null} if no flags are set.
+   */
+  @Nullable
+  @Override
+  public String getOutputDirectoryName() {
+    return flagHash;
+  }
+}